This invention relates to a method of forming a container body such as a drawn container body formed from a metal blank, and to a container body formed by such method. More particularly, it relates to a method which minimizes or avoids wrinkling of metal during forming of the bottom profile in a container body.
It is well known to draw and iron a sheet metal blank to make a thin-walled can body for packaging carbonated beverages. It is also well known that metal manufacturers, can makers and carbonated beverage packagers have had, and continue to have, a goal to reduce the weight of containers and thereby reduce the cost of packaging. One way to reduce weight of can bodies and cans is to form a bottom profile which is capable of strengthening the base wall's resistance against buckling from internal pressure. By so doing, thinner metal can be used to make the can and thereby reduce weight and cost. U.S. Pat. Nos. 3,905,507; 4,099,475; 4,151,927; 4,177,746; 4,294,373 and 5,105,953 are a few of the many which are concerned with bottom profiles and methods of making such profiles.
Many base wall profiles for beverage cans include an annular portion which slopes generally inwardly and downwardly from a bottom portion of the can sidewall and an inwardly projecting dome portion circumscribed by such annular portion. The thinner the metal from which containers are made, the greater the tendency for the metal in the inwardly and downwardly projecting annular wall to wrinkle during redrawing and doming. Clowes U.S. Pat. No. 4,685,322 discloses a method for reducing wrinkling by forming an inwardly (upwardly) projecting annular bead in the bottom wall of the cup which is subsequently redrawn into a container. Elert et al., U.S. Pat. No. 4,372,143 proposes another solution which involves adapting the apparatus used to form the dome so as to support the beveled annular wall with a pressure ring while the dome is being formed.
Another way to reduce can weight is by using smaller diameter lids to close the can bodies. This alternative requires that the center dome on the base profile of the can body also have a smaller transverse diameter in order to facilitate stacking of cans on one another, especially filled cans with small diameter lids on them.
An improved method of forming is needed which minimizes or avoids wrinkling in the bottom profile of redrawn cans, especially for cans made of thin metal and having bottom domes with small transverse diameters.